just got 91 600. did new plugs and oil change with synthetic, which it never had b4
driving down freeway 1 day l8r oil light comes on. get off freeway and when i go to accelerate from light hear grinding sound in top of motor. not sure if its valves or head. has anyone ever heard of this or did my cbr decide to go kawasaki on me[8D]

 

There used to be talk that synthetic oil in an old motor that never had synthetic in it was a bad idea. Something about loosening up the gunk and what not as well as seals and other stuff. 1991 materials should be able to tolerate the chemistry, but old seals exposed to dino oil for 16 years may not.

This may have been true in the old days (my vette still uses dino, all the rest are synthetic), but maybe valve seals or something have taken a dump. Leakdown and compression tests may belp you figure it out. I hope it is something simple like a cam chain issue or something and not valves.

 

Went synthetic on my 93 F-2 this yearI've had no problems, I used an oil flush first, actually feels like it runs better [&:]

 

i don't think the oil has much to do with it. i'm pretty sure that something is up inside your motor and finally decided to break.